I have had days when my activity used to well over 15k and I have even reached 20k at times. It has been a while since I reached 15k because I am finding it very difficult to achieve that.
Moving on,today's activity should have been way over 15k because I was playing a match but unfortunately I couldn't keep my phone with me. I covered a lot of ground throughout the match as I was fielding in the deep and I think that my activity would have been well over 20k.